Lesson 3 of 7 / Nutrition in humans
Absorption, assimilation and the liver
What happens to glucose after it enters the blood?
In this lesson: Trace absorbed nutrients through the hepatic portal vein and explain assimilation.
About 5 min
The key ideaThe hepatic portal vein carries nutrient-rich blood from the small intestine to the liver. The liver processes nutrients before blood carries them onwards.
Hepatic means related to the liver. Follow glucose and amino acids in blood from the intestine; do not confuse this vessel with the duct that carries bile.
Explore the idea
Follow absorbed glucose to the liver
The hepatic portal vein delivers nutrient-rich blood to the liver. Converting absorbed glucose into glycogen is assimilation and storage.
Original flow diagram. Hormonal regulation is studied in homeostasis. Absorbed fat follows mainly the lacteal and lymph route, not this immediate portal route.
Explanation
Digestion produces small soluble molecules that can cross the wall of the small intestine. This crossing is absorption. Glucose and amino acids enter the blood, which carries them away from the absorption surface.
The hepatic portal vein carries blood rich in absorbed nutrients from the small intestine to the liver. It is a blood vessel, not a bile duct. Bile moves from the liver towards the intestine through ducts, so these routes carry different materials in different directions.
Liver cells can remove some glucose and convert it into glycogen for storage. When needed, glycogen can be broken down to glucose and glucose can be released into blood. Glucose is a small sugar; glycogen is a much larger storage molecule made from glucose units.
Assimilation is the use or incorporation of absorbed nutrients by cells. Glucose can be used in respiration, and amino acids can form proteins for growth and repair. Absorption describes entering the transport system from the intestine; assimilation describes what cells subsequently do with the nutrients.
Step by step
- 1
Absorb
Small soluble nutrients cross the intestinal wall into blood.
- 2
Transport
The hepatic portal vein takes nutrient-rich blood to the liver.
- 3
Assimilate
Cells use nutrients, for example by building proteins or storing glucose as glycogen.
Worked example
After a carbohydrate-rich meal
Glucose concentration rises in blood leaving the small intestine. Name the vessel taking it to the liver and describe one way the liver can store it.
One way to explain it
The hepatic portal vein takes the glucose-rich blood to the liver. Liver cells convert glucose into glycogen for storage. Glycogen can later be broken down to glucose when needed.
Why this answer works
- Give the precise vessel name.
- Use the correct direction: intestine to liver.
- Distinguish glucose from its storage molecule glycogen.
Is this true? "The hepatic portal vein carries bile from the liver to the intestine."
It carries blood from the intestine to the liver. Bile travels towards the intestine through bile ducts, which are not blood vessels.